Meningiomas are tumours that grow in the membranes surrounding the brain and spinal cord. Most are slow-growing, but grade 2 and grade 3 meningiomas are more serious and are more likely to come back after treatment. Because these types are less common, there is limited information about what usually happens to patients after surgery. This study brings together evidence from previous research to better estimate how often these tumours return, and how many people remain well or survive five years after treatment. The findings should help doctors, researchers, and patients better understand the outlook for people with grade 2 and grade 3 meningiomas.